This invention relates to a spherical polyamide and a process for preparing the same, more specifically to a spherical polyamide having good quality with a low cost and a process for preparing the same.
Polyamide resin powder has been widely used, in addition to the use of a binder for a plastic magnet and a material for uniformly disperse powder for preparing a master batch, as a powder coating such as an electrostatic coating and a fluidization dip coating, or as an adhesive base material or a hot melt adhesive. However, due to improvement in quality of the powder coating or development to new use, it has been desired to obtain a high quality polyamide resin sphere which is more round than the conventional one, has a grain diameter of 100 .mu.m or less and has a relatively uniform grain size.
For the above purposes, it has been used a method in which a polyamide resin is previously dissolved in a rich solvent and then a poor solvent is added to the solution to precipitate fine powder or a method of chemically pulverizing a polyamide resin by utilizing difference in solubility depending the temperature of a solvent whereby a polyamide resin powder is produced and supplied to a market. However, its cost is high so that the use is limited. Also, there is a problem that many of the commercially available powder are porous state so that they are not uniform sphere. For obtaining an inexpensive polyamide resin powder, it has been carried out a method in which a melted polyamide resin is added dropwise onto a disc rotating with a high speed and scattering it to surroundings to obtain fine powder. However, even when this method is employed, the resulting powder has a porous bulk shape of lava and has a remarkably broad grain distribution so that the use thereof is limited. For example, when it is used as a cosmetic base material, shaving cream or a surfactant for artificial leathers which use high quality polyamide resin powder having more spherical than the conventional ones, small grain size and relatively uniform grain size, expensive chemically pulverized material should be used.
On the other hand, a method of obtaining a granular polyamide resin powder directly from a monomer has been known in Japanese Patent Publication No. 29832/1970, etc., which discloses a method of polymerizing monomers by dissolving them in a liquid substance at high temperature and polymerizing them by using an alkaline catalyst. However, according to this method, an extremely active substance such as metal sodium, etc. is used so that there is a serious problem of causing explosion or a fire. Also, it is difficult to remove impurities in the residue of the catalyst so that the method has not yet been used as a general method for polymerizing polyamide resin powder.